1. Field of the Invention
The present invention relates to resistive wire mass flow meters.
More precisely, the invention relates in particular to mass flow meters intended to be used for measuring the flow of kerosene, for example in aircraft.
2. Description of the Related Art
The applicant has already proposed, in his patent application FR-2.728.071, a hot wire flow meter for measuring a mass flow.
In it, current pulses are sent along the resistive wire for given periods and the cooling speed of the wire between the pulses is measured.
The flow meter comprises processing means which convert the cooling speed thus measured and derive the mass flow from it.
For a given type of fluid, the cooling speed is in fact directly related to the mass flow.
There are however many types of kerosene likely to be used indiscriminately by a same aircraft.
Now, because of their difference in viscosity, their difference in heat conductivity or even their difference in voluminal mass, these different types of kerosene exhibit cooling responses, as a function of the mass flow, which are not identical.
A purpose of the invention is to propose a mass flow meter which is capable of carrying out measurements of mass flow for any type of kerosene by adapting itself to the type of kerosene which is flowing in the pipe in which it makes a measurement.
From EP 210 509 there is already known a measuring device making it possible to determine the mass flow of a fluid and also making it possible, in an independent manner, to determine the composition of the fluid when its speed is known.
This device does not make it possible to solve said problem.
The invention, however, proposes a mass flow meter of the type comprising at least one heating resistive wire placed in the path of a fluid whose flow is to be measured, means of applying heating current pulses to said wire, measuring means for determining its cooling speed between said pulses and for deriving a mass flow from it, characterized in that it comprises two such resistive wires that extend in two fluid passage zones in which the cross sections of said passages being in a given ratio and in that it comprises processing means capable, on the one hand, of determining mass flow measurements for each of said two wires and, on the other hand, of comparing the ratio of the measurements obtained for each of the two resistive wires with a theoretically expected ratio dependent on the given ratio between the passage cross sections, the processing means being capable of deriving from this comparison and from at least one of the measured cooling speeds on the one hand the type of fluid flowing and on the other hand the mass flow of the fluid.
Advantageously, the fluid passage zones are a hollow body in which the fluid flows and a branch which is a diversion with respect to said hollow body.
Preferably, the mass flow meter comprises a profiled body of the aircraft wing type and in that an opening traverses said profiled body, a metal heating wire extending along the length of this opening, the shape of said opening and the incidence of said profiled body in the flow of fluid being such that the boundary layer and the flow to be measured penetrate into said opening in such a way as to avoid or reduce the impacts of particles on the wire.
The invention advantageously applies in particular when the fluid is kerosene, the processing means being capable of deriving the type of kerosene flowing from the comparison used.